The present invention generally relates to transformers, and more particularly to a winding structure for a transformer. The present invention is suitable, for example, for a transformer for use with self-excited (or self-oscillating) switching converters, such as a ringing chalk converter (RCC).
An RCC is known as a typical on/off switching regulator. The switching regulator is a circuit that efficiently regulates a power flow by controlling a time ratio between switching on and off in transistor(s). The on/off type means that a rectifier diode turns off while a switching transistor turns on in a switching regulator. The on/off type transistor stores energy in transformer's primary winding while the transistor turns on, and releases the stored energy to an output side (i.e., a load) via a rectifier diode from transformer's secondary winding while the transformer turns off. The on/off switching regulator is divided into two types; a separately excited type that is activated by an external oscillator, and a self-excited type that switches without an aid of an external oscillator. The latter type is generally referred to as an RCC.
The RCC needs to determine an oscillation frequency and time ratio in order to stabilize an output voltage, and therefore design a transformer considering various parameters including inductance values for primary and secondary windings. Experimentally speaking, an actual transformer that is designed in accordance with conventional theoretic equations would not completely conform to these equations. As a consequence, an attempt to obtain a desired output voltage using a transformer that is designed in accordance with the theoretic equations would cause a transistor to flow infinite collector current Ic over its rated road in a split second due to the excessive low oscillation frequency, possibly breaking down the transistor (while this phenomenon is known as "magnetic saturation"). The actually used transformer used to form an air gap having a gap length of a necessary distance in order to reduce the inductance down to a necessary value by lowering core's effective magnetic permeability. The air gap means core's gap formed at a center pole.
However, the air gap portion has no core connection, and thus causes a leakage magnetic field. The leakage magnetic field might generate, when crossing with a winding, heat in the winding. In particular, a winding having a high turn density (i.e., cohesive turning) has the increased number of turns that cross with the leakage magnetic field, and generates a large amount of heat. The heat increasing the temperature in the power source unit lowers components' reliability, and causing a problem, such as shortening a life of an electrolysis capacitor or another component. The winding generally uses an enamel line that has an upper limit on heatproof temperature, and heat that exceeds the upper limit would disadvantageously break the isolative coat and cause rare short.